A jet engine of an aircraft includes a fan to take air therein, a compressor to take in and compress part of the air taken by the fan, a combustor to mix compressed air generated by the compressor with fuel and to combust the mixture, and a turbine to drive the fan and the compressor by using combustion gas from the combustor, which are all arranged in sequence.
The compressor, combustor and turbine are installed in a main nozzle as a cylindrical partition, and the fan is placed in the upstream side of the main nozzle. Most of the air taken by the fan flows through a bypass flow path which is provided between the main nozzle and a casing (an engine nacelle) covering the outer periphery of the main nozzle. The air (a bypass flow) which has flowed through the bypass flow path is exhausted so as to surround the outside of a core flow (a jet flow) of the turbine, and thus joins to the jet flow.
The area where the jet flow and the bypass flow join to each other becomes a noise source, and thus noise occurs. Various arts are disclosed to reduce such noise.
For example, an art is disclosed in which a microjet nozzle is provided at an exhaust side peripheral edge of the main nozzle, and a microjet is injected from the microjet nozzle to the confluence of the jet flow and the bypass flow (e.g., refer to Non-Patent Document 1).
The microjet nozzle communicates with a fan section or the compressor in the jet engine via pipes which are installed in the periphery of the main nozzle. Part of the compressed air generated by the fan or the compressor is guided through the pipes to the microjet nozzle, and then the compressed air is microjet-injected from the microjet nozzle. By this configuration, the microjet properly mixes the jet flow and the bypass flow, and the noise can be reduced.
In Patent Document 1, a system and a method are disclosed to reduce exhaust noise of a jet engine nozzle having projections (Chevron). The method disclosed in Patent Document 1 includes the steps of generating a first flow of gas by a jet engine, delivering the first flow through a nozzle having a trailing edge perimeter that includes multiple projections extending in the aft direction, and injecting a second flow of a pressurized fluid into the first flow proximate to the projections.
In Patent Document 2, a device is disclosed to reduce exhaust noise of a jet engine by using an oscillating jet.